In general, exhaust gas discharged from an automobile engine (for example, a gasoline engine) includes components such as hydrocarbons (HC), carbon monoxide (CO), nitrogen oxides (NOx). An exhaust gas purification catalyst for removing these components from the exhaust gas is disposed in the exhaust gas passage of an internal combustion engine. Such an exhaust gas purification catalyst is configured by forming a catalyst coating layer on a substrate surface. The catalyst coating layer is constituted by a noble metal catalyst and a carrier that supports the noble metal catalyst.
For this type of exhaust gas purification catalyst, the so-called three-way catalyst is used. In the three-way catalyst, platinum (Pt), rhodium (Rh), palladium (Pd), and the like, are used as noble metal catalysts. Among the noble metal catalysts, Pt and Pd mainly contribute to the ability to purify (by oxidation) hydrocarbons (HC) and carbon monoxide (CO). Further, Rh contributes to the ability to purify (by reduction) nitrogen oxides (NOx).
Examples of conventional art literature related to the exhaust gas purification catalysts using such three-way catalyst include Patent Literature 1-3. For example, the exhaust gas purification catalyst according to Patent Literature 1 is provided with a catalyst coating layer which is formed on a substrate and has a noble metal catalyst such as Pt and Pd and an oxygen storing/releasing material (referred to hereinbelow as OSC (oxygen storage capacity) material) such as CeO2.